There is a ringfort at Curradarra in County Waterford that you cannot see. Standing on the broad hill where it sits, amid ordinary tillage, there is nothing to indicate that a circular enclosure of roughly 35 metres in diameter lies beneath the soil. No earthen bank, no visible ditch, no trace at ground level. It exists, at present, as a cartographic fact more than a physical one.

The evidence for it comes from the first edition of the Ordnance Survey six-inch map, produced in 1840, which records a circular enclosure on the hilltop. Ringforts, which are enclosed farmsteads of the early medieval period typically defined by one or more banks and ditches, were built throughout Ireland from roughly the fifth to the twelfth centuries, and several thousand survive in varying states of preservation. The Curradarra example belongs to a less visible category: sites that were legible to the nineteenth-century surveyors but have since been reduced by centuries of ploughing to the point where the surface shows nothing. Aerial photography or geophysical survey would likely reveal the underlying features, since disturbed soil and buried ditches tend to retain moisture differently from the surrounding ground and show up under the right conditions.